1. Technical Field
The present disclosure relates generally to hydrodynamic face seals.
2. Description Of The Related Art
Spiral groove lift-off seals (also known as hydrodynamic seals or hydrodynamic face seals) have been used successfully for many years in the industrial gas compressor industry. The physics of this type of seal is known and documented.
Generally, the seal assembly involves a high inlet fluid pressure (e.g., high gas density). The high fluid pressure may be located on either an outside diameter of a seal assembly or the inside diameter of a seal assembly, such as generally illustrated in the cross-sectional schematic seal assemblies of FIG. 1A and FIG. 1B, respectively. The seal assembly can be configured either way. The seal assemblies may comprise two rings where a face of each ring is adjacent to one another. A first ring may be a rotational member, also known as a mating ring or rotor, which may rotate about an axis that is generally shared by the two components. A second ring may be a stationary member, also known as a seal ring, and may be movable only in an axial direction. The first ring may contain a plurality of grooves on the face adjacent to the second ring as generally illustrated in FIGS. 1-3. The grooves, which may be spiral in shape, are grooved toward a low pressure side of the first ring. The grooves may have a dam section where the groove ends. A sealing effect around the dead ended grooves can provide a compression of a working fluid, such as gas, resulting in a pressure increase in the groove region. The increase in pressure can causes the faces to separate slightly, which can allow the pressured fluid, such as air, to escape the grooves. A steady state force balance between opening and closing forces is generally achieved at some determinable face separation gap. The seal may operate in a non-contact mode above some threshold rotational speed.
However, when employing conventional hydrodynamic groove technology for the purpose of producing a film riding seal (non-contacting) in sub-ambient atmosphere, such as the outside environment of an aircraft at cruising altitude, the ability for the working fluid to enter the shallow hydrodynamic grooves may be diminished due to the lower density and rarefication of the gas. As the actual volume of the working fluid, such as gas is reduced with the decreasing surrounding system pressure, the resulting hydrodynamic gas film between the rotating mating ring and the stationary seal ring can be significantly reduced. Thin hydrodynamic air films may not be entirely stable and may result in higher heat generation due, for example, to intermittent contact from transient conditions and high vicious shear of the fluid. With respect to aerospace applications, where high surface speed (e.g., 450 feet per second or faster) between the rotating mating ring and the stationary seal ring can be encountered, the aerodynamics of the fluid may further inhibit a working fluid from entering the hydrodynamic grooves.
Among other things, the present disclosure addresses one or more of the aforementioned challenges.